(Animation) Nodes : how to map a rotation to a value between 0 & 1?
the Map Range Node is what you are looking for. It takes the input values (min: 0, max: 360) and maps it to the target values (in your case 0 to 1).

Combine that with a Float Math Node set to modulo of 360. this way you'll only get values between 0 and 360 (540 returns 180 so the map range node will output .5).

separate Euler -> math node -> map range node.

Edit: final nodetree